This invention relates to a gas generating composition which is suitable as a gas generating agent for an air bag system installed in automobiles, airplanes and the like for protecting human bodies.
Various requirements have been put forth on a gas can generating agent for an air bag inflator. It is one of the requirements that a combustion residue after combustion should be reduced. When a combustion residue generated by combustion of a gas generating agent is released outside an inflator, there occur a first problem that a combustion residue having a great heat capacity is contacted with an air bag to hole therethrough, a second problem that a large amount of a floating misty residue might cause an asthmatic passenger to have a fit, and a third problem that a large amount of a floating misty residue might prevent a passengers"" view to make accidents more serious. In order to prevent occurrence of such problems, it is required that a combustion residue should be cooled and filtered through a coolant/filter to remain in an inflator. To this end, however, it is necessary to install a large coolant/filter inside an inflator. In addition, when a large amount of a combustion residue is generated, a coolant/filter is likely to damage, and its function declines in a short time. Accordingly, for decreasing an amount of a combustion residue released outside an inflator, a method of developing a gas generating agent in which an amount of a combustion residue generated is substantially small is most desirable.
Further, it is currently required to more downsize an air bag inflator and to reduce its weight more. However, an existing gas generating agent in which an amount of a combustion reside is large requires an additional component such as a large filter for filtration of a combustion residue or the like. It is therefore difficult to more downsize an inflator itself. From this standpoint as well, a gas generating agent in which an amount of a combustion residue is decreased has been required.
This invention aims to provide a gas generating composition having excellent combustion characteristics as a gas generating agent in which an amount of a combustion residue generated is decreased.
This invention further aims to provide an inflator system using the above gas generating composition.
This invention provides a gas generating composition comprising a fuel made of nitroguanidine, guanidine nitrate or a mixture thereof and an oxidizing agent.
This invention further provides an inflator system using the gas generating composition.
The gas generating agent of this invention is, compared with gas generating agents disclosed so far, by far excellent because of the small amount of the combustion residue, whereby a gas generator can be downsized more to be applied to an air bag system.
The fuel used in this invention is made of nitroguanidine, guanidine nitrate or a mixture thereof. A mixing ratio of nitroguanidine and guanidine nitrate is not particularly limited.
The content of the fuel in the gas generating composition varies with types of an oxidizing agent, a chlorine neutralizer and a binder and an oxygen balance. It is preferably between 35 and 80% by weight, more preferably between 45 and 70% by weight.
Examples of the oxidizing agent used in this invention can include a perchloric acid salt, a nitric acid salt and a mixture thereof.
Examples of the perchloric acid salt and the nitric acid salt can include perchloric acid salts and nitric acid salts containing a cation selected from the group consisting of ammonium, alkali metals and alkaline earth metals. Examples of such perchloric acid salts and nitric acid salts can include ammonium perchlorate, sodium perchlorate, potassium perchlorate, magnesium perchlorate, barium perchlorate, ammonium nitrate, sodium nitrate, potassium nitrate, magnesium nitrate, strontium nitrate and the like. Of these, sodium perchlorate, magnesium perchlorate, sodium nitrate and mixtures thereof are especially preferable because the amount of the residue generated after combustion is small in particular.
As the oxidizing agent, the above-described compounds may be combined in any manner. However, the content of the oxidizing agent in the gas generating agent is preferably between 65 and 20% by weight, more preferably between 50 and 25% by weight.
When ammonium perchlorate is incorporated as the oxidizing agent, a chlorine neutralizer is incorporated for neutralizing a chlorine-type gas such as hydrogen chloride, a chlorine gas or the like for stabilization.
As the chlorine neutralizer, a compound containing a cation selected from the group consisting of alkali metals and alkaline earth metals can be proposed. As the compound containing such a cation, at least one can be proposed which is selected from the group consisting of carbonic acid salts such as sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate and the like; nitric acid salts such as sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate and the like; silicic acid salts such as sodium silicate, potassium silicate, magnesium silicate, calcium silicate, strontium silicate and the like; oxalic acid salts such as sodium oxalate, potassium oxalate, magnesium oxalate, calcium oxalate, strontium oxalate and the like; oxides such as magnesium oxide, calcium oxide, strontium oxide and the like; peroxides such as magnesium peroxide, calcium peroxide, strontium peroxide and the like; cellulose salts such as sodium carboxymethyl cellulose and the like; salts of tetrazole and triazole such as sodium salt, potassium salt, magnesium salt, calcium salt, strontium salt and the like of 5-aminotetrazole; salts of bitetrazole such as sodium salt, potassium salt, magnesium salt, calcium salt, strontium salt and the like of bitetrazole; and so forth.
The content of the chlorine neutralizer in the gas generating composition is preferably between 5 and 40% by weight, more preferably between 10 and 30% by weight.
Further, the gas generating composition can contain, as required, a binder, a combustion catalyst and the like.
Examples of the binder can include inorganic binders such as silica, alumina, molybdenum disulfide, Japanese acid clay, talc, bentonite, diatomaceous earth, kaolin and the like; and organic binders such as metal salts of carboxymethyl cellulose and the like, starch, microcrystalline cellulose, guar gum, polyacrylamide, polyvinyl alcohol, stearic acid metal salts, oligomers and the like.
Examples of the combustion catalyst can include CuO, Cu2O, Co2O3, CoO, Co3O4, Fe2O3, FeO, Fe3O4, MnO2, Mn2O3, Mn3O4, NiO, ZnO MoO3, CoMoO4, Bi2MoO6, Bi2O3 and the like.
It is advisable that the total amount of the additives in the gas generating composition is between 0.1 and 20% by weight.
In the gas generating composition of this invention, the gas composition after combustion can be changed by changing an oxygen balance. For example, it is possible to decrease CO (increase NOx) by changing the oxygen balance to the plus side. Conversely, it is possible to decrease NOx (increase CO) by changing the oxygen balance to the minus side. Accordingly, it is advisable to adjust the oxygen balance in consideration of the safety to human bodies.
The gas generating composition of this invention can be produced by a dry method of mixing a fuel, an oxidizing agent, a chlorine neutralizer, additives and the like in a powdery state or a wet method of mixing the same in the presence of water or an organic solvent.
Further, the gas generating composition of this invention can also be molded into a desired form. For example, it can be compression-molded into a pellet using a pelletizer or into a disk using a disk press machine, a pellet or a disk can be pulverized or granulated using a granulator to form granules or it can be extrusion-molded using an extruder (extrusion-molding machine) to form an extruded pellet (non-perforated, single-perforated or porous shape).
These molding methods can be selected, as required, according to properties and the like which are to be imparted to a molded article of the gas generating composition. For example, in the compression-molding method, inherently, a binder is not required or may be used in a small amount in the molding, so that this is suitable as a method of molding the gas generating composition of this invention. Further, when the extrusion-molding method is employed, it is easier to form an article of a thin web than the compression-molding method. Accordingly, a molded article of a thin web can be obtained with a composition having a low burning rate. Further, the extrusion-molding method is suited for mass-production because it is conducted for a relatively short period of time. Still further, in case of a composition having a high burning rate, a size of a molded article can be increased, making it possible to more improve a production efficiency. Besides, when the extrusion-molding method is employed, a molded article of a non-perforated, single-perforated or porous complicated shape can be produced, so that various combustion characteristics can be imparted.
In the gas generating composition of this invention, the amount of the combustion residue per 1 mol of a gas generated is preferably 12 g/mol or less, especially preferably 10 g/mol or less. This amount of the combustion residue is a total amount of components generated as a solid component and a liquid component in an inflator output temperature which is calculated according to the formulation of the gas generating composition.
The gas generating composition of this invention can be used in any device requiring a gas generating ability of a gun propellant or a rocket propellant. It is especially suited for an inflator system of an air bag installed in automobiles, airplanes and the like for protecting human bodies.
The inflator system of this invention uses the above-described gas generating composition, and they may be applied to a pyrotechnic inflator system, in which all the gas is supplied from a gas generating agent, or a hybrid inflator system, in which gas is supplied from both a compressed gas such as argon and a gas generating agent.
A gas generating method of this invention is a method in which the above-described gas generating composition is burned as a fuel in a gas generator, and it can be applied to various fields utilizing the gas generated by this burning. In the gas generating method of this invention, the gas generating composition is used as a fuel, making it possible to decrease the amount of the combustion residue and improve the gas output.